This invention relates generally to hypodermic needles and syringes, and more particularly the invention relates to a spring locking clip and associated plunger which can be used to convert a plastic hypodermic syringe barrel into a single-use, difficult to reuse, inexpensive syringe made of already medically approved material. For the purposes of this invention the term single-use means that the full maximum dosage placed into the syringe can only be administered one-time. The syringe, however, can administer medication multiple times, each time, however, delivering only a portion of the full medication capable of being drawn into the syringe by a single, full proximal drawing of the plunger rod with respect to the syringe barrel. For short hand notation, the term single-use means a single full dispensing of the entirety of medication drawn into the barrel and includes one or more possible uses, with each use delivering less dosage than the maximum. The cumulative total of delivered dosages obtained by all uses can not exceed the maximum or full dosage drawn into the syringe by a single rearward reciprocation of the plunger rod with respect to the barrel. The syringe is a one-time use syringe when the maximum or full dosage of the syringe (determined by the barrel capacity and/or the position of the spring clip on the plunger) is fully administered in a first and only usage. If that occurs, the spring clip is moved to its full distal position and all reuses are blocked. Where less than the maximum dosage is drawn into the barrel is delivered on the first or succeeding dosage deliveries, the succeeding dosages administered are necessarily less than the maximum. There can be only one full distal movement of the plunger rod, to administer medication made up of individual administrations of medication. The sum of all medication dispensed cannot exceed a single dosage capacity of the barrel of the syringe. In this manner, the device is a "single-use" syringe.
The safe, one-time use and subsequent disposal of hypodermic needles and syringes are immediate concerns in the medical and health professions. Accidental needle stick injuries following use of a syringe pose a significant risk to patients, physicians and nurses. The risk is a source of great anxiety due to the current HIV and hepatitis infection concerns of the general public. Thus, extreme care must be taken in the safe handling and disposal of used needles and syringes. Toward this end, the present invention represents a single-use needle and syringe assembly. After the needle and syringe (hereinafter collectively referred to as the syringe) are used once, the mechanism of the present invention precludes further uses. It will, therefore, be more likely properly discarded than if further use were possible. The possibility of patient to patient cross contamination and drug user to drug user cross contamination are reduced.
The present invention is compact and, therefore, is capable of being implemented into syringes of extremely small size barrel capacity, including syringes capable of administering dosages as low as 0.1 cc. The prior art, on the other hand, as will be more fully explained hereinafter, cannot be easily and/or economically downsized while maintaining the effectiveness of the one-time use only mechanism they describe and, therefore, they have not been commercially introduced in sizes smaller than standard 3 cc syringe bodies. The initial axial location of the locking mechanism with reference to the syringe barrel of the prior art single-use syringes, was the means for limiting a 3 cc conventional syringe to a maximum 1 cc dosage. However, it is clearly desired to have smaller maximum dosage syringes where the size of the syringe, not only the location of the clip, determines the maximum dosage capacity. It should be appreciated, however, that the present invention can also be adapted for use with 3 cc or other maximum dosage syringe barrels and, yet, the present invention has particular applicability to syringes of low dosage barrel capacity even those as low as 0.1 cc capacity.
It is generally recognized that a low cost syringe is essential to meet the needs of less developed countries and to contribute to the reduction of health costs worldwide. A low cost would mitigate syringe re-use now encountered with disposable syringes. The cross contamination resulting from patient to patient reuse of the same syringe would be obviated by a single-use only syringe. It would also reduce patient anxiety resulting from suspected potential infection from prior syringe use.
The present invention provides a simple and inexpensive mechanism for limiting the usage of a syringe (with or without needle) to one-time or single-use only. The syringe is intended to be assembled at the manufacturing facility and provided to the physician (or nurse, patient, etc.) for use. The user fills the syringe with the appropriate medication in the conventional manner, i.e., by withdrawing the plunger with respect to the cylindrical barrel of the syringe, thereby drawing medication through the needle tip and into the chamber of the barrel. According to the present invention, the plunger can be repeatedly reciprocated, for aspirating, prior to loading with medication. Once the user makes the decision that the amount of aspirating reciprocations have been sufficient, a positive movement of the plunger with respect to the barrel ensures the operation of the single-use locking mechanism. Then, again, using conventional technique, the needle is inserted to pierce the patient's skin. The plunger is manually moved with respect to the cylindrical barrel thereby forcing a piston toward the distal end of the syringe. The piston forces the medication out through the needle tip.
During the dosage administration portion of the procedure, according to the present invention, as will be more fully explained hereinafter, a locking spring clip travels along with the plunger shaft and, when it reaches the distal position, locking or contact points are held against the interior sidewall of the cylindrical barrel with the piston abutting the base of the locking spring clip. A second attempted retraction of the plunger with respect to the cylindrical barrel of the syringe is blocked. Thus, no further medication can be pulled into the syringe and, therefore, the syringe is incapable of being used a second time. A simple, inexpensive single-use syringe is provided. The locking mechanism, precluding reuse, is automatic, ire., it operates to block reuse, after aspiration, without a conscious operation by the user to engage its operation.
The design of an economically producible syringe assembly having the feature of single-use and whose safety or one-time use operation is difficult to defeat has been the subject of numerous patents and efforts. Such a syringe should be easy to manufacture and assemble, function in a standard manner, be able to deliver different volumes of fluid, utilize materials which are universally approved for medical use, preferably require standard equipment to manufacture such as used for making syringes in current use, and, importantly, be low in cost.
The present invention accomplishes the above objects by utilizing a new and unique plunger in association and in combination with a new and unique spring locking clip. The plunger comprises a plurality of cylindrical i.e., frusto-conical ratchet teeth or in an alternate embodiment, beads. The spring clip is located by the manufacturer at a particular location along the axis of the plunger so as to limit maximum withdrawal of the plunger, hence dosage of the syringe. According to the preferred embodiment of the present invention, longitudinal spacing is provided between at least two of the ratchet teeth or heads. This allows for plunger withdrawal and advancement without associated spring clip advancement. This, then, allows for aspirating the syringe, prior to loading of the barrel with medication. Also, the use of bead-shaped ratchet teeth, in lieu of our prior disclosed frusto-conical, ratchet teeth, allows for smoother operational motion during plunger withdrawal and a greatly reduced force, during plunger withdrawal, as compared to the withdrawal force of the plunger when the ratchet teeth are cone-shaped or frusto-conical, as in our prior devices.
Currently, there is a specification for the maximum withdrawal force of a plunger in a hypodermic needle/syringe. This was established by the International Standards Organization. Our single-use syringe designs, the subject of parent patent application Ser. Nos. 08/195,302, filed Feb. 14, 1994, and 08/232,749, filed Apr. 25, 1994, were tested and, in some units, found to slightly exceed the specification, although the majority of units had the plunger withdrawal force below the maximum limit of the standard. So as to ensure a high quality product which always satisfies the standard, the present invention was developed. As an alternative, of course, a new standard maximum plunger withdrawal force could be established for single use syringes, since the present "standard" covers disposable syringes which are intended to be and can be repeatedly used.
According to the preferred version of the present invention, the ratchet teeth of the plunger are "bead shaped." The spring clip, then, as the plunger rod is withdrawn, does not, in contrast to our device shown in our prior patent applications, follow each ratchet tooth discontinuity. Rather, the beads allow the spring clip to more smoothly glide over the surface of the beads. The force of withdrawal is reduced and found to be nearly the same as for a reusable syringe and a plunger not having a spring locking clip.
A multiply aspiratable syringe with a spring locking clip is desirable. The invention disclosed in the prior patent applications was not designed to allow for multiple aspirations (i.e., multiple reciprocations of the plunger to draw air into and then expel it from the barrel) but to a limited extent aspiration was possible in those situations where the initial withdrawal and projection of the plunger advanced the spring clip to a position less than the full distal or forward position.
The present invention is intended to allow for multiple aspirations. The device uses a gap between ratchet teeth so that any movement of the plunger, when the spring clip is between ratchet teeth, i.e., within the gap, does not cause the spring locking clip to advance. Of course, the amount of gap between ratchet teeth determines the amount of aspirating.
The use of this new plunger and spring locking clip blocks reuse of the syringe. The construction can be incorporated into syringes of even 0.1 cc barrel size, without any loss of efficiency or safety. The operating mechanism of the present invention allows extremely small volumetric capacity of syringes to be manufactured, without loss of performance. In contrast, the locking mechanisms of prior art single-use syringes operate by use of different mechanisms and, therefore, very small volume syringes cannot be manufactured. The present invention is economical to manufacture, has tamper-proof features, administers medication using conventional techniques, is made of medically approved materials, and can be made with standard equipment.
The present invention has the withdrawal force of the plunger within acceptable limits of multiple-use syringes and, yet, is a single-use syringe. The mechanical withdrawal of the plunger having bead-like teeth is a smoother operation than that which is present with frusto-conical ratchet teeth. Also, the use of one or more aspirating gaps, between ratchet teeth, allows the syringe to be selectively and repeatedly aspirating.
It is a feature of the present invention to provide the thumb-contacting portion of the syringe plunger as a break-apart disc such that, after use, the user of the syringe can simply bend or twist and remove the thumb-contacting disc and, thereby, further disable the syringe from a subsequent reuse. The ease of removal of the thumb-contacting portion of the plunger shaft from the syringe also serves as a means for tracking inventory of the syringes.